1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) control circuit and a control method thereof, and more specifically, to a control circuit and a method thereof that detects image edges of frames to reduce memory size by decreasing saved pixel data when executing the overdriving procedures.
2. Description of the Prior Art
Liquid crystal display (LCD) panels are mass-produced products applied to the field of computers, monitors, and TVs. The operation principle of an LCD is to vary voltages dropped on two terminals of liquid crystal cells in order to change a twisted angle of the liquid crystal cells. The transparency of the liquid crystal cells is changed for achieving the desired objective of illustrating images. Therefore, accurately and appropriately controlling the voltages between two terminals of liquid crystal cells is a key point for showing images rapidly and clearly.
It is well known by those skilled in the art that overdriving procedures are usually executed to reduce response time of the liquid crystal cells as images vary rapidly. Please refer to FIG. 1. FIG. 1 is a block diagram of an LCD control circuit 100 according to the prior art. The control circuit 100 receives a gray level value of every pixel and determines the voltage applied on the two terminals of the liquid crystal cell corresponding to a pixel unit in accordance with the gray level value difference of the pixel unit between a current frame and a previous frame. As FIG. 1 shows, the control circuit 100 includes a buffer circuit 110, a frame memory 120, and a driving-decision circuit 130. Gray level values Din of pixels are inputted into the control circuit 100 and then delivered to the driving decision circuit 130 and the frame memory 120 respectively through the buffer circuit 110. The symbol Gn in the figure shows the data is the gray level value of pixels in the current frame. The frame memory 120 records inputted gray level values and outputs a pre-saved gray level value Gn-1 that corresponds to the pixels in the previous frame to the driving decision circuit 130. Next, the driving decision circuit 130 compares the gray level value Gn of the current frame and the gray level value Gn-1 of the previous frame and then compares the difference between these two gray level values with the value saved in a look-up table to determine whether the control circuit 100 has to execute overdriving procedures and therefore whether a corresponding voltage will be dropped on the liquid crystal cells when the overdriving procedure is executed. Finally, the driving-decision circuit 130 outputs a driving voltage setting Sout to a voltage supply circuit to provide the voltage dropped on two terminals of the liquid crystal layer.
Because the frame memory 120 has to save gray level values of all pixels in a frame, the memory size needs to be large enough to include the gray level values of all pixels in a frame. However, the larger the memory size is, the more expensive it becomes.